The present invention is a knife edged or chisel edged front plate for trench boxes, the knife edge allowing the front end of the trench box to penetrate earth, sand and debris while rigidly supporting and spacing the adjacent trench box walls from each other. By gripping the earth in penetration with the box, the entire box is stabilized.
Unlike prior art front plates which merely provided a barrier against cave-in intrusion of debris into the box, the present invention provides a smooth unbroken bottom with skin surfaces which assist penetration into the earth with the trench box and which assists in sealing the end of the box against entry of debris and water. This is a valuable function when the box is working, for example, in sand and water bearing strata. During the installation in the ground, the weight of the trench box and engagement of the knife edged front plate with the ground urges the front plate into the ground as the box itself drops in the trench opening. The knife edge on the front plate facilitates location and penetration with the box.
Prior art front plates were usually tubes coupled over shaft-like or tubular step extensions and pinned therethrough against withdrawal. These served as spacers between the sides of the box and where debris barriers were needed a plate was usually welded or fastened between the upper and lower tubes. The tubes met stiff resistance to extra penetration into the earth and there was a poor fit or closure of the make-shift plates against the sides of the box and the flooding-in or cascading-in of debris at the front corner was common in certain types of ground and particularly flowable ground. In the prior art structures the engagement of transverse struts or tubes with the earth applied strains to the trench box panels at the connections of tubes to panels. The prior art front plates with tubes is best shown in the U.S. Pat. No. 3,992,887 to Walter A. Fisher and large lower surface contact areas are seen in the front structurals of the U.S. Pat. No. 3,212,270 to O. H. Benintend. In the U.S. Pat. No. 4,090,365 of A. J. Nieber, the front plate included blunt structural horizontal elements and simple reinforced sheets welded between the structural elements.
Accordingly, the present invention is intended to solve the problem presented by such blunt front plates by providing a digging or shear-functioning earth penetrating bottom which vastly improves trench box performance in flowing ground. This is of substantial significance in a trench box system which is under constant relocation and repositioning as it continuously progresses to shore an open hole or trench as it progresses and with the hole or trench being filled behind it. A chisel edge is presented carrying the structural weight and thrust of the box and the smooth interior and exterior closure surfaces on the chisel edge are relatively smooth and unbroken in relation to the earth in avoidance of frictional resistance to ground penetration of the front plate and against removal while accomplishing a substantial seal of the box at the front against the intrusion of debris and water.
At least one panel skin is usually provided which is fastened to the structural support elements on the outside and may be an extension of the bottom closure panel. An inner skin may be applied to present a smooth inner surface rising from the chisel edged bottom. The object of the panel skins, where used, is to prevent intrusion of debris through the framing of the front panel. The front panel of the present invention also establishes a lineal fastening to the adjacent trench box panels in contrast to prior art "point" or "knuckle" fastening and thus rigidifies the trench box at the front.
Other objects including economy, rigidity improvement and rugged serviceability with good load conducting characteristics will be appreciated by those skilled in the art as the description proceeds.
General Description
In general, a new, useful and inventive knife edged front plate is the subject of the present invention. The front plate attaches to the front end of a trench box and between the spaced apart vertical walls or panels thereof to form a penetrating and gripping barrier against intrusion of earth, water and debris from the front. At the rear end of the trench box, the barrier is unneeded since the rear end usually includes elevated panel spacers which straddle or bridge high between the trench box panels in prevention of collapse but which allow work to progress in the box and the pipe, for example, to trail behind the trench box until fill is pressed into the opening behind the moving trench box on closing in the pipe, tubing, or culvert work.
The front plate of the present invention is thus positioned transverse of the wall panels of the trench box and is removably secured to each of the panels substantially at the leading or front edges. The fastening of front plate to panels is in a vertical line contact. The front plate includes a structural support grouping made up of horizontal structural members and vertical structural members and which may be covered on one or both sides by panel skins. The vertical and horizontal skeletal members are connected as by welding to each other and the lowermost horizontal member includes a plurality of depending spaced apart triangular shaped gusset members and the gusset members are in spaced apart parallel position and each in a vertical plane. These gusset members, when covered, provide rigid structural support for the knife edged bottom of the front plate. "Vertical " and "horizontal" as used herein has reference to the orientation in use shown in the FIG. 1. An outer vertical smooth skin may be applied over the vertical and horizontal structural skeletal members as shown and may depend to cover the outer edges of the gusset members. The outer skin where used is secured to the structural elements and gusset members as by welding and the outer skin, where used, extends to the lowermost apex of the gusset members. An inner skin may be also affixed as by welding to the structural skeleton and extends downward and in parallel registry to the outer skin stopping short of covering the gusset members. The gusset members then are closed in by a closure plate which is attached to the gusset plates and to the lower horizontal structural member and also closes on the outer vertical skin at the bottom. It will be appreciated that the outer vertical skin may extend upwardly only to cover the lower horizontal member or may extend fully to the upper horizontal member. Triangular frontal corner plates reinforce and stabilize the juncture as between vertical and horizontal elements and are secured in place as by welding. Fastener openings run through the vertical end structurals and the corner plates and skins, where used, to provide support for fasteners running through the front plate and thence through mounting plates, brackets or lugs fixed or secured to complement the vertical box elements along the leading edges of the trench box panels. The vertical edges of the front plate are reinforced by the in-line bracket attachment to the trench box panels. While other forms of fasteners or disconnects are available, the preferred fastening is through the openings, as illustrated, and thence to simple brackets as angles or channels fastened snuggly as by bolts and nuts through the preformed openings and secured to the trench box channels. The advantage is in better rigidity achieved by the connection of front plate to adjacent spaced apart trench box panels while performing the role of spreaders in an improved way. The front plates of the present invention are also easily removed for dismantling from the trench box when unneeded. Other forms of front plate may use the same mounting and fastening means and be substituted for the front plate of the present invention by using common brackets and fasteners.
As will be appreciated, the front plate of the present invention closes the front end of the trench box with a stabilizing wall or barrier and the lower knife edge is formed skeletally by the gusset members and covered by the outer skin and closure plate to provide a ground engaging earth penetrating shoe or bottom which utilizes the weight of the total box as a driving tamp applied at the digging edge. In use, this type of front plate is extremely effective in loose shifting earth and water supported sand. In mud type earths, the barrier is effective against water and gravel debris which would likely intrude into the trench.